1. Field of the Invention
The present invention pertains to a Radio Frequency Receiver in general, and more particularly to a Super-Regenerative Radio Frequency Receiver and its data receiving method.
2. Description of the Related Art
An On-Off Keying (OOK) Radio Frequency Receiver is commonly found in a remote control application, such as a low-speed-command-control electronic device or toy car. In FIG. 1, an OOK modulated signal is presented. In the figure, clearly, an OOK modulated signal is a carrier frequency been modulated in a binary code. During an OOK modulated signal in transmission, on a transmitter, corresponding to a low period of the binary code, a low period OOK modulated signal containing no carrier frequency is transmitted. Corresponding to a high period of the binary code, a high period OOK modulated signal containing carrier frequency is transmitted. On a receiver, the strength of the transmitted signal varies depending upon the distance between the transmitter and the receiver. Then, an oscillator in the receiver will oscillate faster or slower according to the strength of a received signal. From the oscillating speed of the oscillator, the receiver distinguishes logic 1 from logic 0. Apparently, it is difficult for the receiver to differentiate a weak signal from logic zeros, and it is easy for the receiver to differentiate a strong signal from logic zeros. Therefore, a better performance can be achieved by setting the receiver to its most sensitive condition if the receiver can be controlled to operate normally without running to a saturation condition.
FIG. 2 demonstrates a widely used Super-Regenerative Radio Frequency Receiver in a block diagram. As depicted in FIG. 2, a Super-Regenerative Radio Frequency Receiver 20 contains an oscillator 202, capacitor 204, low-pass filter 206, and slicer 208, where the low-pass filter 206 contains a resistor 210 and a capacitor 212. The Super-Regenerative Radio Frequency Receiver is described by parts as follows.
The oscillator 202 produces an oscillating output signal according to a radio frequency signal and a quench signal. The radio frequency signal, the quench signal, and the oscillating output signal in FIG. 2 are depicted in FIG. 3 respectively. The quench signal is a saw-wave signal with a frequency close to 400 hertz (Hz). As the radio frequency signal at a low period that is at logic 0 of the binary code, the oscillating frequency of the oscillating output signal will slow down, and as the radio frequency signal a high period that is at logic 1 of the binary code, the oscillating frequency of the oscillating output signal will increase.
The capacitor 204 is an alternating current (AC) coupling capacitor; thereby, it filters out a direct current (DC) component of the oscillating output signal, and by-passes a AC component of the oscillating output signal. The low-pass filter 206 filters out an unwanted AC component of the oscillating output signal to obtain a desired frequency band of the oscillating output signal. The slicer 208 is used to slices the oscillating output signal. Then, after the oscillating output signal passes the slicer 208, an output data is obtained.
However, due to the big capacitance of the capacitor 204 in the Super-Regenerative Radio Frequency Receiver 20, it is not practical to fabricate the capacitor in an integrated circuit (IC). Similar to the resistor 210 and the capacitor 212, for a high resistance and a high capacitance are required to build a low-pass filter, the resistor 210 and the capacitor 212 of the low-pass filter 206 are also not practical to be built in an IC. As a result, an extra size IC would be made if the Super-Regenerative Radio Frequency Receiver 20 were built in an integrated circuit.
Referring to FIG. 4, the block diagram depicts another commonly used Super-Regenerative Radio Frequency Receiver. From FIG. 4, the Super-Regenerative Radio Frequency Receiver 40 contains Low Noise Amplifier (LNA) 402, oscillator 404, Envelope Detector 406, low-pass filter 408, slicer 410, two Automatic Gain Control (AGC) filters 412, 416, two voltage-to-current transformers 414, 418. The AGC filters 412, 416 consist of low-pass filters to obtain the rectifiered signal energy level. In the Super-Regenerative Radio Frequency Receiver 40, when the radio frequency signal contains various amplitudes of components and causes the oscillator to output various amplitudes oscillating signals to the Envelope Detector 406, the wide range varying signal outputted from the Envelope Detector 406 causes the common mode voltage of the output signal of the low-pass filter 408 varying in a big range, and causes the low-pass filter 408 and the slicer 410 saturated. As a consequence, the output of the slicer 410 contains unacceptable errors. In additional to the various amplitudes of the radio frequency components resulting in the saturation of the low-pass filter 408 and the slicer 410, the variation during the Super-Regenerative Radio Frequency Receiver 40 fabrication procedure will make the saturation problem worse. Therefore, the various amplitudes of the radio frequency components and the fabrication procedure reduce the sensitivity of the Super-Regenerative Radio Frequency Receiver 40.